Constant torque nut



Aug. 10, 1954 G. A. DMITROFF CONSTANT TORQUE NUT Filed March 22, 1951 (Ittomegs Patented Aug. 10, 1954 UNITED STATES PATENT OFFICE CONSTANT TORQUE NUT George A. Dmitroff, Milford, Conn.

Application March 22, 1951, Serial N 0. 217,010

3 Claims. .1

This invention is concerned with screw-threaded fastenings and more particularly relates to a constant torque nut.

In the past, whenever a person was tightening a nut upon a screw or bolt by means of a wrench or similar tool, care had to be exercised that too much force was not exerted on the wrench .during the tightening, which would tend to strip the threads from either or both the nut and the bolt. The danger in such a situation was present to a greater extent whenever a long handled wrench was used, whereby considerable leverage or torque could be applied. In those cases where several nuts were used to bolt down one object to another or to a base, it was additionally necessary that all the nuts be tightened to approximately the same degree to prevent the creation of undesirable and unequal stresses and strains due to variations in nut tightening torques. Such a situation would exist in the tightening of a cylinder head to an engine block, for example. The use of a tension or torque wrench has been resorted to in many cases to prevent the application of an overpowering torque to an individual nut or to provide for the application of approximately equal torques to a multiplicity of nuts. However, the use of a torque wrench is limited to nuts of 'a certain size and more often than not, the torque wrench will not fit the size nuts in question. Additionally, quite often the torque wrench will be mislaid temporarily, or be borrowed by another, or be lost, wherein time will be wasted looking for it. In any event, it was another special tool which had to be carried in a mechanics tool kit, which was already overloaded to begin with, to be used in those situations where the application of excessive torque might be hazardour. to the safety or operation of a machine.

Another disadvantage of the tension or torque wrenches now in common use is that they cannot be used to good advantage or at all in crowded or cramped quarters wherein suflicient leverage room is not provided. The physical configuration and the dimensions of the average torque wrench are such that it is impossible to use the wrench unless considerable room is readily available for the movement of its handle during the application of the desired leverage.

Still another disadvantage of the usual torque wrench, which arises indirectly as a result of the difficulty of using the average torque wrench in cramped quarters, lies in the fact that, although they may be used in such cases by means of cooperating adaptors and/or drives, the reading obtained on the torque wrench is not correct unless its drive is directly over the nut or bolt which is being tightened. For example, if an adaptor were to be used of the type which oifsets the drive from directly over the nut or bolt, a correction factor would have to be determined and used with that particular offset adaptor. If a universal drive coupling were to be used with the torque wrench, a continually varyin correction factor would be necessary which would make the use of a torque wrench in such a case a practical impossibility.

An object of the present invention is to provide a constant torque nut wherein the torque control is present in the nut itself to permit its use in crowded or cramped quarters.

A further object of the present invention is to provide a constant torque nut which may be used directly with any and all kinds of adaptors and/or drives whereby the torque control is not affected and wherein the use of correction factors is unnecessary.

A purpose of the present invention is to provide a constant torque nut which may be used with an ordinary wrench and which cannot be overloaded to an extent as to strip the threads of the nut or the associated bolt.

Another purpose of the present invention is to provide constant torque nuts which may be tightened to a predetermined tension which cannot be exceeded, whereby several nuts may be simply tightened to the same degree without requiring special tools or care to avoid undesirable and unequal stresses and strains.

Still another purpose of the present invention is to provide a constant torque nut which may be designed for a maximum tightening effect without the use of tension or torque Wrenches or other similar special tools.

A feature of the present invention is the provision of a fastening nut which may be tightened by an ordinary wrench to a predetermined amount and wherein the attempted application of excess torque will be made known to the mechanic.

Another feature of the present invention is the provision of a fastening nut which cannot be tightened beyond a predetermined amount, no matter how much overpowering force be applied.

Still another feature of the present invention is the provision of a fastening nut wherein the tightening torque cannot exceed a preset maximum but wherein the loosening torque may reach any physical limit possible to provide for an easier removal from the bolt.

' Other purposes and features of the present invention will become apparent from the following description referring to the drawing, in which:

Figure 1 is a view in elevation, partly in cross section, showing the constant torque nut of the present invention as threaded to a stud.

Fig. 2 is a full cross-sectional View taken on the line 2-2 of Fig. 1.

Fig. 3 is an exploded drawing, showing the various parts of the constant torque nut of the present invention.

Fig. 4 is a detail drawing of the hexagonal ring and molded insert portion of the constant torque nut of the present invention.

Fig. 5 is a detail drawing of the internally threaded nut portion of the constant torque nut of the present invention.

Fig. 6 is a cross-sectional view taken along a similar line to that of 2 but showing the configuration of the parts during the application of a nut tightening torque.

In the preferred embodiment of the invention as shown in the drawing, the constant torque nut Hi comp-rises an inner shell or nut portion it? which may be internally threaded, as at Hi, to any desired. pitch or diameter, whereby it may be threaded to a correspondingly externally threaded bolt or stud S. The inner nut portion i2 is externally formed with a series of ratchetlike teeth or serrations it which extends circum ferentially around the nut portion from a flanged base 18 of larger diameter to the upper end of the nut portion I2. The nut is preferably made of steel but may be made of other materials such as brass, aluminum, etc, depending on the nature of the stud S and the requirements of the particular situation.

A driving ring 2d having an external hexagonal or other shape adapted to be engaged by a wrench or other similar tool and turned thereby,

has integrally bonded to its cylindrical inner wall 22 a liner of a moldable, resilient rubber-like material 24. The inner face of the liner of moldable material 24 is formed with a series of resilient ratchet-like teeth or serrations 26 which are very similar to the serrations I6 but of a slightly larger size so that the ring may he slipped over the nut portion 12 with their respective ratchet-like teeth in close contact, as shown in Fig. 2, to act similar to a multiple pawl arrangeface of the upper end of the nut portion 12 and provides a seat for a split lock-ring or lookwasher 3B which may be made of a flexible material, such as spring steel, for example, and snapped into place in the groove 28 to prevent the ring 2i) from slipping off the nut portion [2, as shown in Fig. 1.

When torque is applied to the hexagonal outer portion of the ring l2 in the direction of the arrow in Fig. 6, the ring and its ratchet-like teeth or serrations 26 will tend to ride up slightly on the corresponding teeth I6 of the internally threaded nut portion until sumcient traction or friction has developed and then the ring will turn the internally threaded nut portion l2 and advance it around and along the stud S. This will continue until the flange iii of the nut portion l2 abuts the fiat surface in which the stud is secured. At that moment, the resistance ofiered by the nut to rotation will increase sharply until it reaches a point at which it is equal to the driving force transmitted between the engaged ratchet teeth. The nut then will be securely threaded to the stud with the required torque and the inclined ratchet teeth will begin to slip to prevent any increase in applied torque.

It is to be pointed out that the constant torque of the nut of the present invention is the torque which actually exists and is present during the slipping movement of the tightening ring 20 around the nut portion 12, which constant torque is, of course, transmitted to and exerted on the stud S. If a torque wrench of the usual type were to be applied to the tightening ring 29 and force were to be exerted thereon in an eifort to apply additional or excess torque to the nut portion 12 and to the stud S, the reading on the torque wrench would build up to the constant torque as a maximum which would be determined by the construction and characteristics of the serrations or teeth of the constant torque nut itself. Upon continued turning of the torque wrench, the reading would drop practically to zero as the cooperating serrations or teeth i6, 26 would suddenly slip past each other, but would again cyclically rise to its constant torque value before dropping again, as rotation continued. This building-up and dropping-off of torque would occur twelve times for a full rotation of the tightening ring 20 around the nut portion i2 and thus there would be twelve torque pulses per complete turn for the illustrated embodiment of the invention. This would be transmitted to the arm of the mechanic who was tightening the nut or bolt. Throughout all this, the torque which is being applied through the constant torque nut to the stud S remains constant and is entirely unaffected.

This slipping will be immediately apparent to the mechanic who is thus made aware that the proper torque has been applied. However, should the mechanic be unaware of this fact and should continue applying force and rotating the hexagonal outer surface of the ring 28, nothing will happen except an idle slipping of the ratchet teeth 23 over the ratchet teeth it. As a result, the amount of applied torque cannot be increased by rotating the hexagonal outer surface too much.

It is to be appreciated that the point at which the slipping of the ratchet teeth over each other occurs may be controlled by several factors. First, the internal clearances between the respective teeth may be varied whereby slipping may take place correspondingly sooner or later. Second, the angles of the faces of the ratchet teeth and their heights may be varied to increase or decrease the gripping relationship thereof and to thus modify the slipping point of the teeth. Third, the properties and characteristics of the materials used, such as the elasticity of the insert 24, for example, will affect the yielding of the teeth under load to change the maximum torque which can be applied before slippage occurs.

When it is desired to remove the constant torque nut I0 from the stud S, the hexagonal outer portion of the ring 29 is turned in the opposite direction. Consideration of Figs. 2 and 6 will reveal that, when the rotation is in this direction, the sharply inclined or abrupt faces of the ratchet teeth oppose each other and thus substantially precludes the possibility of slippage of the ratchet teeth in this opposite direction. As a result, a much greater turning force may be applied during loosening of the constant torque nut than could be applied during the tightening thereof, due to the unidirectional features of the driving engagement between the ring member and the nut portion [2.

If desired, the snap-ring may be dispensed with and the ring 20 may be held in place on the nut portion l2 by a flange at the upper end, somewhat similar to the flange It]. This flange could be made originally of a diameter to permit the assembly of the ring 20 on the nut i2 and then could be peened-over, spun-over, or otherwise enlarged, which would prevent the ring member 26 from slipping off the nut portion i2 and would thus give to the constant torque nut the advantages of having a non-removable outer ring which would prevent tampering with the nut. Additionally, this would reduce the number of parts required from three to two and would permit an easier and quicker assembly and provide for a greater economy and a simpler production as regards the manufacturing aspects.

Although the constant torque nut it has been described herein as having the resilient ratchetlike teeth formed in a liner bonded to the ring member, it is to be appreciated that the liner with the resilient teeth could be bonded to the nut portion to cooperate with ratchet-like teeth formed on the inner surface of the ring member. Two bonded liners could be used but it is not as preferable.

From the above, it will be seen that the problems of applying too much torque during the tightening of an individual nut and of applying equal torques to a group of nuts have been solved by providing this slipping arrangement of parts whereby torque can be applied only up to a predetermined maximum which cannot be exceeded. At the same time, the slipping parts have been so arranged that slippage occurs only during the tightening of the nut and not during the loosening thereof so that any possible amount of torque may be applied to loosen the nut.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. A constant torque nut comprising an internally threaded nut portion for engagement 1:

teeth being formed of compressible material, said ratchet teeth being formed with a gradually inclined face and a substantially radially inclined face, whereby said gradually inclined faces will be engaged and drive the nut portion during the threading of said nut portion on the externally threaded members and will be capable of graddaily compressing and slipping out of driving engagement when excess torque is applied to said ring member to enable the transmission of torque to said nut portion up to a predetermined maximum and to prevent the transmission of excess torque thereto, and said substantially radially inclined faces will be engaged to positively drive the nut during the removal of said nut portion from the externally threaded members to enable the transmission of all the applied torque to nut portion.

2. The invention as defined in claim 1, wherein said ratchet teeth on the outer surface of said nut portion are formed integrally therewith and said ratchet teeth on the inner surface of said ring member are formed in a resilient liner bonded tosaid ring member.

3. A constant torque nut comprising an internally threaded nut portion for engagement with externally threaded members; a ring member surrounding said nut portion and including external means for providing driving engagement by a tool; means securing said ring in cooperative relation with said nut; a set of ratchet teeth on the outer surface of said nut portion; and a set of ratchet teeth on the inner surface of said ring member for driving engagement with said first named ratchet teeth, one set of ratchet teeth being formed of compressible material, said ratchet teeth each being formed with a radial face and a gradually inclined face forming an angle of less than with the radial face, said gradually inclined faces engaging during the threading of said nut portion on the externally threaded members and driving the nut during application of normal turning torque and the compressible teeth gradually compressing and slipping out of driving engagement when excess torque is applied to said ring member and preventing the transmission of said excess torque to the nut, and said radial faces engaging in non-slipping engagement during. the removal of said nut portion from the externally threaded members to enable the transmission of all the applied torque to said nut portion.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,723,389 Thiel Aug. 6, 1929 2,125,270 C'onover Aug. 2, 1938 FOREIGN PATENTS Number Country Date 258,472 Great Britain Sept, 23, 1926 324,581 Great Britain Jan. 30, 1930 

